Problem: The sum of $6$ consecutive even numbers is $78$. What is the fifth number in this sequence?
Answer: Call the first number in the sequence $x$ The next even number in the sequence is $x + 2$ The sum of the $6$ consecutive even numbers is: $x+ (x + 2)+ (x + 4)+ (x + 6)+ (x + 8)+ (x + 10) = 78$ $6x + 30= 78$ $6x = 48$ $x = 8$ Since $x$ is the first number, $x + 8$ is the fifth even number. Thus, the fifth number in the sequence is $16$.